Method and system for adjusting a measurement cycle in a wireless receiver

ABSTRACT

Methods and systems for measuring wireless signals are described. The method includes generating a velocity estimate that includes a speed and a direction of a wireless receiver. A change in the velocity estimate is detected and how frequently the wireless signal is measured is adjusted according to the change detected in the velocity estimate. Systems may include wireless receivers that include an accelerometer that is operable to generate a velocity estimate that includes speed and direction of the wireless receiver. The wireless receivers may also include a processor operable to adjust a measurement period of the wireless signal in the wireless receiver according to a rate of change in the velocity estimate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No: 11/327,036, filed on Jan. 6, 2006 now U.S. Pat. No. 7,973,710,which is a continuation of U.S. patent application Ser. No: 10/912,516(now U.S. Pat. No. 7,012,564), filed on Aug. 5, 2004. Theabove-referenced United States patent applications are all herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to positionlocation systems. More particularly, the invention relates to a methodfor adjusting a measurement cycle in a satellite positioning systemsignal receiver.

2. Description of the Related Art

Global Positioning System (GPS) receivers use measurements from severalsatellites to compute position. GPS receivers normally determine theirposition by computing time delays between transmission and reception ofsignals transmitted from satellites and received by the receiver on ornear the surface of the earth. The time delays multiplied by the speedof light provide the distance from the receiver to each of thesatellites that are in view of the receiver.

More specifically, each GPS signal available for commercial use utilizesa direct sequence spreading signal defined by a unique pseudo-randomnoise (PN) code (referred to as the coarse acquisition (C/A) code)having a 1.023 MHz spread rate. Each PN code bi-phase modulates a1575.42 MHz carrier signal (referred to as the L1 carrier) and uniquelyidentifies a particular satellite. The PN code sequence length is 1023chips, corresponding to a one millisecond time period. One cycle of 1023chips is called a PN frame or epoch.

GPS receivers determine the time delays between transmission andreception of the signals by comparing time shifts between the receivedPN code signal sequence and internally generated PN signal sequences.These measured time delays are referred to as “sub-millisecondpseudoranges”, since they are known modulo the 1 millisecond PN frameboundaries. By resolving the integer number of milliseconds associatedwith each delay to each satellite, then one has true, unambiguous,pseudoranges. A set of four pseudoranges together with a knowledge ofabsolute times of transmission of the GPS signals and satellitepositions in relation to these absolute times is sufficient to solve forthe position of the GPS receiver. The absolute times of transmission (orreception) are needed in order to determine the positions of the GPSsatellites at the times of transmission and hence to compute theposition of the GPS receiver.

Positioning systems, such as GPS, have fostered numerous applicationsthat involve tracking people and assets. Various systems provideperiodic location of a fixed asset, notification of proximity topre-requested services, on-demand location identification, or continuoustracking of the location of a person or asset. Presently, such systemsengage in satellite measurements at a device being tracked on a scheduleunrelated to the relevance of the tracking information. This results intracking the device continuously or tracking the device too infrequentlyto be effective. Continuous tracking directly results in increased powerconsumption in the device. Conversely, accessing the device tooinfrequently results in decreased accuracy and tracking performance.

Therefore, there exists a need in the art for a method that provides forthe automatic adjustment of a measurement cycle in a satellitepositioning system signal receiver.

SUMMARY OF THE INVENTION

A method for adjusting a measurement cycle in a satellite signalreceiver is described. In one embodiment, a notification is received atthe satellite signal receiver in response to at least one of aroute-critical event and a motion-change event. A frequency of themeasurement cycle is then adjusted in response to the notification. Inone embodiment, the route-critical event comprises the satellite signalreceiver being within a threshold distance of a route-critical locationalong a route. A motion-change event comprises a change in motion of thesatellite signal receiver with respect to a threshold value.

In another embodiment, a mobile receiver includes a satellite signalreceiver and a processor. The satellite signal receiver is configured tomeasure pseudoranges from the mobile receiver to a plurality ofsatellites as part of a measurement cycle. The satellite signal receiveris further configured to periodically execute the measurement cycle. Theprocessor is configured to adjust the frequency of the measurement cyclein response to a notification indicative of at least one of aroute-critical event and a motion-change event. In one embodiment, themobile receiver further includes a sequential estimation filter, such asa Kalman filter, and the satellite signal receiver is further configuredto apply pseudoranges to the sequential estimation filter as part of themeasurement cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a block diagram depicting an exemplary embodiment of aposition location system in which the present invention may be utilized;

FIG. 2 is a flow diagram depicting an exemplary embodiment of a methodfor adjusting a measurement cycle in a satellite signal receiver inaccordance with the invention; and

FIG. 3 is a flow diagram depicting another exemplary embodiment of amethod for adjusting a measurement cycle in a satellite signal receiverin accordance with the invention.

To facilitate understanding, identical reference numerals have beenused, wherever possible, to designate identical elements that are commonto the figures.

DETAILED DESCRIPTION

A method and apparatus for adjusting a measurement cycle in a satellitepositioning system signal receiver is described. Those skilled in theart will appreciate that the invention may be used with various types ofmobile or wireless devices that are “location-enabled,” such as cellulartelephones, pagers, laptop computers, personal digital assistants(PDAs), and like type mobile devices known in the art. Generally, alocation-enabled mobile device is facilitated by including in the devicethe capability of processing satellite positioning system (SPS)satellite signals, such as Global Positioning System (GPS) signals.

FIG. 1 is a block diagram depicting an exemplary embodiment of aposition location system 100 in which the present invention may beutilized. The system 100 comprises a mobile receiver 102 incommunication with a server 108 via a wireless communication network 110(e.g., a cellular communication network). For example, the server 108may be disposed in a serving mobile location center (SMLC) of thewireless communication network 110. The mobile receiver 102 obtainssatellite measurement data (e.g., pseudoranges, Doppler measurements)with respect to a plurality of satellites 112. The server 108 obtainssatellite navigation data (e.g., orbit trajectory information, such asephemeris) for at least the satellites 112 in view. Position informationfor the mobile receiver 102 is computed using the satellite measurementdata and the satellite navigation data.

Satellite navigation data, such as ephemeris for at least the satellites112, may be collected by a network of tracking stations (“referencenetwork 114”). The reference network 114 may include several trackingstations that collect satellite navigation data from all the satellitesin the constellation, or a few tracking stations, or a single trackingstation that only collects satellite navigation data for a particularregion of the world. An exemplary system for collecting and distributingephemeris is described in commonly-assigned U.S. Pat. No. 6,411,892,issued Jun. 25, 2002, which is incorporated by reference herein in itsentirety. The reference network 114 may provide the collected satellitenavigation data to the server 108.

The mobile receiver 102 is configured to receive assistance data fromthe server 108. In one embodiment, the assistance data comprisesacquisition assistance data. The acquisition assistance data maycomprise expected pseudoranges or pseudorange models, expected Dopplerdata, and like type acquisition aiding information known in the art.Exemplary pseudorange models and details of their formation aredescribed in commonly-assigned U.S. Pat. No. 6,453,237, issued Sep. 17,2002, which is incorporated by reference herein in its entirety. Forexample, the mobile receiver 102 may request and receive acquisitionassistance data from the server 108 and send satellite measurement datato the server 108 along with a time-tag. The server 108 then locatesposition of the mobile receiver 102 (referred to as the mobile stationassisted or “MS-assisted” configuration). Acquisition assistance datamay be computed by the server 108 using satellite trajectory data (e.g.,ephemeris or other satellite trajectory model) and an approximateposition of the mobile receiver 102. An approximate position of themobile receiver 102 may be obtained using various position estimationtechniques known in the art, including use of transitions between basestations of the wireless communication network 110, use of a last knownlocation of the mobile receiver 102, use of a location of a base stationof the wireless communication network 110 in communication with themobile receiver 102, use of a location of the wireless communicationnetwork 110 as identified by a network ID, or use of a location of acell site of the wireless communication network 110 in which the mobilereceiver 102 is operating as identified by a cell ID.

In another embodiment, the assistance data comprises satellitetrajectory data (e.g., ephemeris, Almanac, or some other orbit model).Upon request, the server 108 may transmit satellite trajectory data tothe mobile receiver 102 via the wireless communication network 110.Alternatively, the mobile receiver 102 may receive satellite trajectorydata via a communications network 142 (e.g., a computer network, such asthe Internet). Notably, the satellite trajectory data may comprise along term satellite trajectory model, as described in commonly-assignedU.S. Pat. No. 6,560,534, issued May 6, 2003, which is incorporated byreference herein in its entirety. Having received the satellitetrajectory data, the mobile receiver 102 may locate its own positionusing the satellite measurement data (referred to as the “MS-Based”configuration). In yet another embodiment, the mobile receiver 102 maylocate its own position by obtaining ephemeris directly from thesatellites 112, rather than from the server 108. That is, the mobilereceiver 102 locates its own position without assistance from the server108 (referred to as the “autonomous” configuration).

The server 108 illustratively comprises an input/output (I/O) interface128, a central processing unit (CPU) 126, support circuits 130, and amemory 134. The CPU 126 is coupled to the memory 134 and the supportcircuits 130. The memory 134 may be random access memory, read onlymemory, removable storage, hard disc storage, or any combination of suchmemory devices. The support circuits 130 include conventional cache,power supplies, clock circuits, data registers, I/O interfaces, and thelike to facilitate operation of the server 108. The I/O interface 128 isconfigured to receive satellite navigation data from the referencenetwork 114 and is configured for communication with the wirelesscommunication network 110. In addition, the I/O interface 128 may be incommunication with the network 142.

In one embodiment, the position location system 100 includes a travelinformation server 144. The travel information server 144 is configuredto provide map information and the like for providing travelinstructions from an origin to a destination (a “route”). The mobilereceiver 102 may request and receive routing information from the travelinformation server 144 through the network 142 or through the wirelesscommunication network 110 via the server 108. Such travel informationservers are well known in the art.

The mobile receiver 102 illustratively comprises a GPS receiver 104, awireless transceiver 106, a processor 122, an I/O interface 150, and amemory 120. In one embodiment, the mobile receiver 102 includes asequential estimation filter, such as a Kalman filter 138. In oneembodiment, the mobile receiver 102 also includes a motion measurementdevice 152. The GPS receiver 104 receives satellite signals from thesatellites 112 using an antenna 116. The GPS receiver 104 may comprise aconventional GPS receiver. The wireless transceiver 106 receives awireless signal from the wireless communication network 110 via anantenna 118. The GPS receiver 104 and the wireless transceiver 106 arecontrolled by the processor 122. The I/O interface 150 may comprise amodem or like-type communication interface for communicating with thenetwork 142.

The processor 122 may comprise a microprocessor, instruction-setprocessor (e.g., a microcontroller), or like type processing elementknown in the art. The processor 122 is coupled to the memory 120. Thememory 120 may be random access memory, read only memory, removablestorage, hard disc storage, or any combination of such memory devices.Various processes and methods described herein may be implemented usingsoftware 140 stored in the memory 120 for execution by the processor122. Notably, the Kalman filter 138 may be implemented via the software140. Alternatively, the mobile receiver 102 may implement such processesand methods in hardware or a combination of software and hardware,including any number of processors independently executing variousprograms and dedicated hardware, such as application specific integratedcircuits (ASICs), field programmable gate arrays (FPGAs), and the like.Notably, the Kalman filter 138 may be implemented using hardware or acombination of hardware and software.

Position of the mobile receiver 102 may be located using a navigationmodel in a well-known manner. Notably, in the general satellitenavigation problem, there are nine unknowns:

-   -   Three position unknowns: x, y, z    -   Three velocity unknowns: {dot over (x)}, {dot over (y)}, ż{dot        over ( )}    -   Three clock unknowns: t_(c), t_(s), f_(c)        where t_(c) is the common mode timing error (usually a        sub-millisecond value in GPS), t_(s) is the absolute time tag        error, and f_(c) is the frequency error in a local oscillator        within the mobile receiver 102. One or more of the variables may        be known or estimated based on a-priori information (e.g., t_(s)        may known if the mobile receiver 102 is calibrated to precise        GPS time). One or more of the unknown variables may be solved        for using satellite measurement data from the mobile receiver        102 in a well-known manner.

In another embodiment, a history of information may be used tocontinuously produce a filtered position result. The incorporation ofhistory relies upon a formal model or an informal set of assumptionsregarding the tendency of the mobile receiver 102 to move from positionto position. By placing bounds on the motion of the mobile receiver 102(and the behavior of a clock in the mobile receiver 102), filtering timeconstants may be selected that adequately track receiver dynamics, yetallow improved accuracy through the averaging process. Another advantageof filtering techniques is that the mobile receiver 102 may continue tooperate when insufficient satellite measurements exist to createindependent solutions. For purposes of clarity by example, an aspect ofthe invention is described with respect to a Kalman filter. It is to beunderstood, however, that other types of sequential estimation filtersmay be employed that are known in the art, such as Batch Filters.

Notably, position of the mobile receiver 102 may be located using theKalman filter 138. The Kalman filter 138 includes a plurality of states,such as position states, velocity states, clock states, and frequencystates. The satellite measurements are applied to the Kalman filter 138,which is configured to provide position upon request. Multiplemeasurement sets may be used to update the states of the Kalman filter138. The update weighs both the current state information and themeasurements to produce new state information. For further detailsregarding operation of the Kalman filter 138, the reader is referred tocommonly-assigned U.S. patent application Ser. No. 10/790,614, filedMar. 1, 2004, which is incorporated by reference herein in its entirety.

In operation, the mobile receiver 102 periodically executes ameasurement cycle, where pseudoranges from the mobile receiver 102 tothe satellites 112 are measured by the GPS receiver 104. In oneembodiment, the measurement cycle further includes application of thepseudoranges to the Kalman filter 138. The measurements are used toperiodically locate position of the mobile receiver 102. Position may belocated using the Kalman filter 138 or using a navigation model. Forexample, the mobile receiver 102 may be traveling along a route as setforth by the travel information server 144. Progress of the mobilereceiver 102 along a route may be tracked by periodically locating itsposition. Notably, the frequency of the measurement cycle and thefrequency of the position location cycle (position fix cycle) may be thesame or may be different (e.g., measurements may be obtained more ofless often than position computations). In another example, the mobilereceiver 102 may be tracked (i.e., location of the mobile receiver 102may be periodically located) without having a route designated by thetravel information server 144.

As discussed below, the frequency of the measurement cycle may beautomatically adjusted in response to a course-change event, such as aroute-critical event, a motion-change event (heading and/or speed), orcombination of such events. Note that the term “course” is used in ageneral sense to include heading and/or speed. The GPS receiver 104 mayreceive a notification of such an event from the processor 122. Notably,a route-critical event may be triggered when the mobile receiver 102 iswithin a threshold distance of a route-critical location along a route(e.g., a route designated by the travel information server 144). Aroute-critical location may be any location or group of locationsrelevant to travel along a route such as, for example, an approachingintersection, an approaching fork in the road, an approaching maneuver(e.g., a required turn to stay on the established route), an approachingoff-ramp, an approaching freeway exit, and like-type travel events.

A motion-change event may be triggered in response to a change in motionof the mobile receiver 102 with respect to a threshold value. In oneembodiment, a motion change event is detected by the Kalman filter 138.The Kalman filter 138 may be configured with states that continuouslyestimate velocity and heading of the mobile receiver 102. A change insuch states beyond a threshold may be used to indicate a change invelocity and/or heading of the mobile receiver 102. If the Kalman filter138 detects changes in one or more of such velocity and heading states,the Kalman filter 138 may trigger a motion-change event. In anotherembodiment, a change in motion of the mobile receiver 102 may bedetected using one or more motion measurement devices 152. The motionmeasurement devices 152 may comprise an accelerometer, a speedometer,compass, flux-gate compass, and like-type motion measurement, motiondetection, and direction measurement devices known in the art, as wellas combinations of such devices. For a given type of motion measurement,a threshold may be established in accordance with a given metric todelineate whether the mobile receiver 102 has transitioned from onemotion state to another. In yet another embodiment, a combination of theKalman filter 138 and motion measurement devices 152 may be used totrigger the motion-change event.

The frequency of the measurement cycle may be increased or decreased inresponse to a triggered event. For example, the frequency of themeasurement cycle may be increased in response to a route-criticalevent. By increasing the frequency of the measurement cycle, the mobilereceiver 102 obtains measurements more often to achieve greater trackingaccuracy. This may assist the user of the mobile receiver 102 tonavigate through the route-critical location. In another example, thefrequency of the measurement cycle may be decreased in response to amotion-change event indicative of a stationary condition. If the mobilereceiver 102 is in a stationary condition, the mobile receiver 102 mayconserve power by performing less measurements.

FIG. 2 is a flow diagram depicting an exemplary embodiment of a method200 for adjusting a measurement cycle in a satellite signal receiver inaccordance with the invention. The method begins at step 202, where anominal frequency is designated for the measurement cycle of thesatellite signal receiver. That is, the satellite signal receiverexecutes the measurement cycle at a predefined, nominal frequency. Thenominal frequency for execution of the measurement cycle is a designparameter based on desired tracking accuracy versus power consumption.The nominal frequency may be set such that sufficient measurements existfor a desired frequency of position computations. For a given positionfix frequency, less measurements are required if the Kalman filter 138is employed, since the Kalman filter 138 is capable of producing acontinuously filtered position result based on previous measurements.For example, the measurement cycle may be performed once every fiveseconds nominally.

At step 204, a determination is made as to whether a route-criticalevent has occurred. If not, the frequency of the measurement cycle ismaintained at the nominal frequency and step 204 is repeated. If aroute-critical event has occurred, the method 200 proceeds to step 206.At step 206, the frequency of the measurement cycle is increased. In oneembodiment, the frequency of the measurement cycle may be increased fromthe nominal frequency to an increased frequency value. In anotherembodiment, an increased frequency value may be selected from aplurality of increased frequency values, and the frequency of themeasurement cycle may be increased to the selected value. Selection ofan increased frequency value may be based on the type of route-criticalevent (e.g., an approaching intersection may engender less of anincrease in frequency than an approaching sequence of required turns).

At step 208, a determination is made as to whether the route-criticalevent is complete. If not, the frequency of the measurement cycle ismaintained at the increased frequency and step 208 is repeated. If theroute-critical event has completed, the method 200 proceeds to step 210.At step 210, the frequency of the measurement cycle reverts back to thenominal frequency value. The route-critical event may be deemedcomplete, for example, if the mobile receiver 102 is outside aroute-critical location by a threshold distance. Alternatively, aroute-critical event may be deemed complete after a predetermined timeperiod has elapsed. The method 200 may be repeated for variousroute-critical events.

For purposes of clarity by example, the method 200 has been describedwith respect to adjustment of the measurement cycle from a nominalvalue. It is to be understood, however, that the frequency may beadjusted from a current value (whether the nominal value, or not) to anyother increased value.

FIG. 3 is a flow diagram depicting another exemplary embodiment of amethod 300 for adjusting a measurement cycle in a satellite signalreceiver in accordance with the invention. The method 300 begins at step302, where a nominal frequency is designated for the measurement cycleof the satellite signal receiver. At step 304, a determination is madeas to whether a motion-change event has occurred. If not, the frequencyof the measurement cycle is maintained at the nominal frequency and step304 is repeated. If a motion-change event has occurred, the method 300proceeds to step 306.

At step 306, the frequency of the measurement cycle is adjusted inresponse to the motion-change event. The adjustment of the measurementcycle may be based on the type of motion-change event. For example, ifthe motion-change event indicates that the mobile receiver 102 hastransitioned into a stationary state, the frequency of the measurementcycle may be decreased from a nominal value. In another example, if themotion-change event indicates that the mobile receiver 102 has changeddirection, the frequency of the measurement cycle may be increased froma nominal value. By increasing the frequency of the measurement cycle,the mobile receiver 102 obtains measurements more often to achievegreater tracking accuracy. This may assist the user of the mobilereceiver 102 to navigate through a critical location as indicated by thechange in direction. Those skilled in the art will appreciate thatvarious other types of motion changes may be used to trigger increasesor decreases in the frequency of the measurement cycle at step 306.

At step 308, a determination is made as to whether the motion-changeevent is complete. If not, the frequency of the measurement cycle ismaintained at the increased frequency and step 308 is repeated. If themotion-change event has completed, the method 300 proceeds to step 310.At step 310, the frequency of the measurement cycle reverts back to thenominal frequency value. The motion-change event may be deemed complete,for example, if the mobile receiver 102 after a predetermined time haselapsed or after a predetermined time has elapsed without the occurrenceof another motion-change event. The method 300 may be repeated forvarious motion-change events.

For purposes of clarity by example, the method 300 has been describedwith respect to adjustment of the measurement cycle from a nominalvalue. It is to be understood, however, that the frequency may beadjusted from a current value (whether the nominal value or not) to anyother increased value. Furthermore, those skilled in the art willappreciate that a combination of the method 200 of FIG. 2 and the method300 of FIG. 3 may be performed to adjust the frequency of themeasurement cycle in response to either a route-critical event or amotion-change event.

Method and apparatus for adjusting the measurement cycle of a satellitesignal receiver has been described. In one embodiment, the measurementcycle of the satellite signal receiver is adjusted in response to anexternal event (referred to as a course-change event), such as aroute-critical event, a motion-change event, or a combination of suchevents. The frequency of the measurement cycle may be increased ordecreased depending on the type of event that triggered the adjustment.The invention may be used to automatically adjust the measurement cyclefrequency according to the user's current need. For example, a user'sneed of greater tracking accuracy through a route-critical location ismet by automatically increasing the frequency of the measurement cycle,which provides more measurements. A user's need of less trackingaccuracy while in a stationary state is met by automatically decreasingthe frequency of the measurement cycle, which conserves more power.

In the preceding discussion, the invention has been described withreference to application upon the United States Global PositioningSystem (GPS). It should be evident, however, that these methods areequally applicable to similar satellite systems, and in particular, theRussian GLONASS system, the European GALILEO system, combinations ofthese systems with one another, and combinations of these systems andother satellites providing similar signals, such as the wide areaaugmentation system (WAAS) and SBAS that provide GPS-like signals. Theterm “GPS” used herein includes such alternative satellite positioningsystems, including the Russian GLONASS system, the European GALILEOsystem, the WAAS system, and the SBAS system, as well as combinationsthereof.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for measuring a wireless signal,comprising; generating a velocity estimate comprising a speed and adirection of a wireless receiver; detecting a change in the velocityestimate; and adjusting how frequently the wireless signal is measuredaccording to the change in the velocity estimate.
 2. The method of claim1, comprising: determining a degree of accuracy for the velocityestimate; and adjusting how frequently the wireless signal is measuredaccording to the degree of accuracy for the velocity estimate.
 3. Themethod of claim 1, wherein the velocity estimate is generated using asequential estimation filter.
 4. The method of claim 1, whereingenerating the velocity estimate comprises: storing a history of thevelocity estimate; and updating the velocity estimate according to thehistory of the velocity estimate.
 5. The method of claim 1, whereindetecting a change in the velocity estimate comprises detecting a changein the speed of the wireless receiver.
 6. The method of claim 1, whereindetecting a change in the velocity estimate comprises detecting a changein the direction of the wireless receiver.
 7. The method of claim 1,wherein the velocity estimate is generated using at least onepseudorange.
 8. The method of claim 1, wherein the velocity estimate isgenerated using one or both of a Kalman filter and a Batch filter. 9.The method of claim 1, wherein the velocity estimate is generated usinga motion measurement device.
 10. The method of claim 9, wherein themotion measurement device is at least one of an accelerometer, aspeedometer, a compass and a flux-gate compass.
 11. A wireless receiverfor measuring a wireless signal, comprising: one or more processorsconfigured to generate a velocity estimate comprising speed anddirection of the wireless receiver and adjust a frequency at which thewireless signal is measured by the wireless receiver according to adetected change in the velocity estimate.
 12. The wireless receiver ofclaim 11, wherein the one or more processors are configured to adjustthe frequency in response to a degree of accuracy for the velocityestimate.
 13. The wireless receiver of claim 11, wherein the one or moreprocessors comprise one or more of a sequential estimation filter, aKalman filter and a Batch filter to generate the velocity estimate. 14.The wireless receiver of claim 11, wherein the one or more processorsare configured to generate the velocity estimate by storing a history ofthe velocity estimate and updating the velocity estimate according tothe history of the velocity estimate.
 15. The wireless receiver of claim11, wherein the one or more processors are further configured to detectthe change in the velocity estimate by detecting a change in the speedof the wireless receiver.
 16. The wireless receiver of claim 11, whereinthe one or more processors are further configured to detect the changein the velocity estimate by detecting a change in the direction of thewireless receiver.
 17. The wireless receiver of claim 11, wherein theone or more processors are configured to generate the velocity estimateby using at least one pseudorange.
 18. The wireless receiver of claim11, wherein the one or more processors comprise a motion measurementdevice.
 19. The wireless receiver of claim 18, wherein the motionmeasurement device is at least one of an accelerometer, a speedometer, acompass and a flux-gate compass.
 20. A wireless receiver for measuring awireless signal, comprising: an accelerometer operable to generate avelocity estimate comprising speed and direction of the wirelessreceiver; and a processor operable to adjust a measurement period of thewireless signal in the wireless receiver according to a rate of changeof the velocity estimate.